Transistor question

I used the search function and couldnt find anything....
Could someone explain Generally how a transistor amplifies voltage.
When I come off my board to run a motor or something.....dont I need to use a transistor to drive it....?
And how does that transistor do that.
Maybe I'm wrong.
D.

A transistor don't actually amplify a voltage, but it can control a larger voltage, like a relay. You can have a small signal (3.3 or 5 V) control a larger voltage source (12 V or more). The best transistor to use for controlling a motor would be a MOSFET.

Ok....a transistor is a electronic pilot operated flow contro....a little gate in which the base is the gate master....
But in the above circuit from the Wikapedia site you suggested....
Why wouldnt power go from V+ to Vout...thru the resistor and capacitor...
It doesnt need to go thru the transistor.....does it...
It has a parallel pathway .....

Wait a minute....whats the diff between V+ and Vin....."?
Are they both supply and just labled differently to confuse me...
D.

Click to expand...

It may seem that way, but no. V+ is the positive power supply.
Vin indicates the input. In this case, a changing voltage.
Current cannot flow through a capacitor, so only a changing voltage is seen on the other side. This means that there could be a voltage potential on the capacitor. A constant voltage is not passed through, but a changing voltage is seen by all the devices attached to it.
In the diagram, R1 and R2 set the voltage of the gate on the transistor so it is halfway on. A changing voltage on the input passes through the capacitor and changes the voltage on the gate.
The change in voltage causes a change in current at the base, which the transistor amplifies and different amounts of current flow through the transistor from collector to emitter. The different amount of current flowing shows up as a change in voltage at the ends of the resistors, Rc and Re. Again, the changing voltage is passed through the capacitor and shows up as a change in voltage on the output.

The diagram shows a signal amplifier. A small changing voltage is amplified to a larger changing voltage.
I said that the capacitor blocks a steady DC voltage where there is no current flowing.
When the voltage changes on the input, it creates a different voltage potential on the capacitor (Cin). This voltage potential causes some electrons to either be attracted or repelled to/from the capacitor. This small change is noticed by the base on the transistor and the flow from the collector to emitter is changed. The flow of electrons changes the potential on Cout, which produces the amplified signal.

Yes . A transistor is a variable resistor . You can use a transistor in many ways .
One of the way is using a transistor in series with a motor for example . When the transistor is off then the resistance is very high (20 Mohm ++ ) so no current will flow. When the transistor is on then the resistance is < 1ohm so current will flow (the transistor isn't limited to on/off !! , you can have any value inbetween). Basically you are using your transistor as a variable switch.

Another way of using it is as you said 'variable voltage regulator ' in a sense .
where you arrange the transistor in a voltage divider configuration .
A resistor (1k for example) is R1 and your transistor will be R2 . And when you send a variable current to the base of the transistor then the output between the collector and R1 will bounce relative to the current supplied to the base .
(this is all crudely said , but it's how the transistor works)

Wait a minute....whats the diff between V+ and Vin....."?
Are they both supply and just labled differently to confuse me...
D.

Click to expand...

V++ is the power supply voltage (your positive terminal of the battery or whatever)
The Vin is the small signal that you supply to the base of the transistor which is 'amplified' , increased in magnitude (within the limits of the power supply voltage !)